Interference Cancellation and Detection for MAC with Two Users - Interference Cancellation Using Space-Time Processing and Precoding Design - page 26

Multi−User, 2 bits/sec/Hz

10 −1

MUD in [5]
Our Scheme
No interference

10 −2

10 −3

10 −4

10 −5

10 −6

10 −7

10 12 14 16 18 20 22 24

Signal to Noise Ratio (dB)

Fig. 2.5 Comparison of our scheme and MUD in [ 5 ] for 2 users each with 4 transmit antennas

where τ 1 is a constant. From ( 2.104 ), we know that

}≤ τ 2 ρ − 6 Pr { σ = 0 (2.110)

τ 2 is a constant. Substituting ( 2.109 ) and ( 2.110 )in( 2.108 ), we get

where

d 2 → d 2 ) ≤ (τ 1 + τ 1 )ρ − 6

Pr ( (2.111)

Using ( 2.111 ), it is easy to show that the diversity d ≥ 6. Also we can show that

diversity d 6. So the diversity for User 2 is 6, i.e., full diversity. Therefore, we

can achieve full diversity for both Users 1 and 2 which can also be confirmed by the
simulations in the next section.
Note that whenwe complete the detection of the symbols of User 2, we can remove
the effects of User 2 using the detected symbols of User 2 and re-detect the symbols
of User 1. Simulation results show that such an iteration improves the coding gain.
Finally, a similar antenna selection method at the receiver results in a diversity of
NM for a general case of N transmit and M receive antennas.

≤